Apparatus for propylene polymerization



July 6, 1965 J. s. scoGGlN APPARATUS FOR PROPYLENE POLYMERIZATION FiledMay 5l, 1961 PROPYLENE CATA LYST 43 POLYMER INVENTOR.

J, S. SCOGGIN HYDROGEN A TTORNEVS United States Patent O 3,193,360APPARATUS FR PROPYLENE PDLYMERHZATHN ack S. Sceggin, Bartlesville,Okla., assigner to Phillips Petroleum Company, a corporation of DelawareFiled May 31, 1961, Ser. N 113,681 1 Claim. (Cl. 23--2S3) This inventionrelates to a method and apparatus for polymerizing propylene to solidpolymer.

Propylene can be polymerized in the liquid phase in the presence of anorganometallic catalyst to form a solid resinous polymer which is usefulin the formation of lms, laments and a variety of molded items such asbottles and similar containers. The catalyst used ordinarily includes anorganornetal of a nontransition metal of Groups I to ill of the periodicsystem; for example, aluminum, beryllium, zinc, magnesium, lithium orsodium having at least one hydrocarbon radical attached thereto and theremaining valences, if any, satisfied by halogen or hydrogen. Complexorganometal such as alkylaluminum plus an alkali metal, for example,lithium aluminum tetrapropyl, can sometimes be used. The organometal isused in conjunction with a transition metal compound, preferably ahalide of a metal of Groups IV to Vi of the periodic system, forexample, titanium, vanadium, zirconium, hafrniurn, thorium, uranium,niobium, tantaiuin, chromium, molybdenum or tungsten. The chlorides oftitanium are preferred. As the commercialization of polypropylenedevelops, it is essential that improvements and simpliiication be madein both the polymerization process and the methods of polymer recovery.The eld ot solid thermoplastics is highly competitive and polypropylene.must compete with well established resins such as polyethylene.

Although an inert liquid diluent is normally employed in propylene; andother oleiin polymerization processes, according to my invention thepolymerization is carried out with liquid propylene as the reactionmedium. A Vertical tower is employed as the reactor and the introductionof propylene vapor into the bottom of the tower eliminates the need forinternal agitation by mechanical means. T he reaction mixture is cooledby boiling the liquid propylene and the temperature of the process canbe controlled by regulating the pressure in the tower. According to myinvention, propylene is polymerized by contacting an o;- ganometalliccatalyst with a body ot boiling liquid propylene in a verticallyelongated reaction zone, passing propolyene vapor formed by the boilingof said liquid propylene upward through a separation zone in Contactwith down-flowing liquid propylene while maintaining a flowing film ofliquid propylene over the vertical walls of the tower section whichencompasses said separation zone. In this manner, polymer accumulationswhich would normally tend to build up in the vapor space above thereaction mistura are avoided since polymer particles which wouldotherwise contact and adhere to the tower wall are washed by the flowinglm of liquid back into the body of liquid propylenc. Propylene vapor iswithdrawn from the top of the vapor space and at least a portion thereofis circulated to the bottom ot the body of boiling propylene to agitatosame. Also, a portion of the vapor which is removed from the body ofliquid propylene is condensed and reiluxed in contact with the risingvapors. Particulate polymer solids are withdrawn from the bottom of thereaction zone.

The apparatus of my invention is a reactor which comprises, incombination, a closed vertically elongated shell having a lower liquidreaction section, an intermediate vapor section and an upper reduxsection, means for introducing liquid into the vapor section againstsaid shell, vapor-liquid contacting means in said reflux section, meansfor circulating vapor from the top of said reilux section into thebottom of said reaction section, means for refluxing condensed vaporthrough said vapor-liquid contacting means, and means for withdrawingpolymer solids from the bottom of said reaction section.

It is an object of my invention to provide an improved method for thepolymerization of propylene to solid polymer. Another object is toprovide a simiplied reactor for the polymerization of propylene. Afurther object of my invention is to provide a process for thepolymerization of propylene which requires no mechanical agitationwithin the reaction zone and provides a reaction eiliuent from whichpolymer can be readily recovered. Another object is to provide a methodof carrying out a propylene polymerization in a tower reactor withboiling liquid propoylene as the reaction medium while avoiding theproblem of polymer accumulation in the vapor space immedi ately abovethe body of boiling propylene. Other objects, advantages and features ofmy invention will be apparent to those skilled in the art from thefollowing discussion and drawing which illustrates the improved reactorof my invention with a portion of the shell in the separation sec tionbeing cut away to show the trough, bale and spray means which incombination with the other features of the tower reduce the tendency ofpolymer to build up in this separation zone.

While a wide variety of organometallic catalyst systems can be employedfor the polymerization of propylene to solid resin, I prefer to use acatalyst which includes the combination of an aluminum alkyl and atitanium halide, preferably a dialltylaluminum chloride or bromide inwhich the alkyl groups have from one to eight carbon atoms each andtitanium chloride. The catalyst system most preferred is diethylaluminumchloride and titanium trichloride. This catalyst can be used verysuccessfully to polymerize propylene to high molecular weight resin attemperatures and pressures which permit liquid propylene to be employedas reaction medium. Generally the weight ratio of the titanium halide tothe alkylaluminum is in the range of about 0.5:1 to 20:1. Under thepolymerization conditions employed in my process, polypropylene isformed in the reactor in solid particulate form and is removed from thereactor' by gravitational settling. A relatively quiescent zone ismaintained in communication with the lower portion or" the reaction zoneso that polymer particles can settle therein and accumulate for removalfrom the reactor in a high solids concentration. For example, in thereaction suspension, the solids content can be maintianed at about 25percent while removing an efiluent stream of settled polymer solids andliquid propylene having a solids content of percent. These solids can beconcentrated further in a compression auger to about percent. Thecatalyst is removed from the eluent polymer by washing with a suitablesolvent such as isopropyl alcohol and the unreacted propylene can beremoved in a separate liashing step upstream from the catalyst removaloperation or it can be removed in admixture with the catalyst solventwith subsequent separation of these two materials for propylenerecovery. If desired, the polypropylene can be further extracted with asuitable solvent such as normal heptane for removal of an atacticpolymer fraction. Depending upon the polymerization conditions employedmore or less of such atactic polymer `is `formed and it may be desirableto effect such a removal of amorphous polymer in order to improve theflexural modulus of the finished product.

The details of both the method and apparatus or" my invention can bestbe understood by referring to the drawing. For purposes of clarity, thisdrawing has been simplied in regard to the feed streams to the reactorand a number of variations in the method of feeding materials to thereactor other than the specific embodiment shown are possible as will4be evident from the following discussion. The reactor is made up ofthree principal secy Y Y 3 tions which are a lower reaction section 10,an intermedi- "at'e' "separation" section 1I, and an upper vrefluxsection/12. The lower reaction sectioniof the reactor which contains theliquid body of boiling propylene is preferably an upright cylindricalshell yhaving a length to diameter ratio inthe range of about 3:1 to10:1. The intermediate separation sectionv denes a 'vapor spaceimmediately above the 'reaction section and is preferably a continuation'of the shell'which forms the reaction section. The separation' sectionordinarily will have a length to diameter ratio in the' range of about1:1'to 5:1. TheV upper reflux section 'positioned immediately above theseparation section contains means for contacting the rising vapors withliquid propylene. 'In'the Vembodiment shown in the drawing, tthi"s"sepa`r'ation`se'ction containsv Contact packing-material "such-asRaschig rings or Berl saddles. Top closure member `13 closes the top Vofreflux section 12 while bottom closur'e4 memberli forms the'bottorn ofreaction section 10. Fresh-propylene is introducedthrough conduit '16and the catalyst is introduced into the lbody of liquid propylenethrough conduit 17. Ordinarily the catalyst 4components are introducedseparately; for example, the `titanium tichloride'can' be introduced asa slurry in liquid propylene which forms a part of the feed material andthe diethylaluminum chloride can be introduced as a solution in ayhydrocarbon such as normal decane. Since a relatively small amount ofcatalyst is employed on a weight basis, very little of the normal'decanesolvent is required. In `addition-to any fresh propylene which isintroduced withfthe catalyst, other -fresh propylene can be introducedVdirectlyto Vthe liquidbodyof propylene innthe reaction #sectionfasrequired to maintain the desired liquid level in.` the reactor.

The polymerization reaction is exothermic and the heat 0f reactionisremoved by vaporizing'vthe propylene from .y the liquid body. Byregulating the pressure within the reactorytakinginto consideration thepresence of hydrogen,the desired temperature can be maintained.Temperatures within the range of O'to 190 F. can-be'em- Iployed although'the-preferred temperature' is ordinarily v'in the'rangeof 60 to 150 F.VThepressure within the f reactorestablishes thedesired temperature andcan' range anywhere from' 50 to 760 p.s.i.a;,preferably about 130 to.300 -p.s.i.a. The amount of catalyst 'employed can' varyfsubstantially.but'normally'about 0.0001 to 0.001 pound 'lofdieth'ylaluminum'chloride are used per pound of propylene. feed.-Theratio of titanium trichloride tol diethylaluminum-chloride'i is'preferably in the range of about lzllto 4.5 :lon a weight-basis.Hydrogen can be used Vinlthe process to control the=melt index of thefinished rproduct. Ordinarily, the hydrogen concentration is in theirangeof about 0.305'to 1 mole percent basedon the liquid propylenein"thelreactorandlpre-ferably is not over 0.5 f percent. -The presenceof hydrogen tends to increase the melt index of the polymer.

2 Vapors leaving' theboiling'liquid body of propylene, the upper levelof which is shownlin the cutaway portion 'of reaction section 310,pass-upwardly through separation "section`11 and are contacted bydroplets of propylene introducedthrough spray 18 which is fed by conduit16. LBecause of the turbulence within the reactor, the rising -Yvaporsof'propylene tend to'carry with them finely divided '-polymer'particleswhich couldcause fouling on the reactor walls. `According to ourinvention, these polymer particlesar'e' scrubbed from the rising vaporsby the spray Yof li'quid 'propylene and' fouling 'of the reactor wallsis prevented by maintaining a film of downward flowing propylene alongthe wall sections most likely to be contacted by the polymer particles.This iilm yof liquidprovpylene can be formed by multiple spraysimpingingagainst `th'e"wall of the reactor at the top ofthe separation sectionor' by some similar liquid distribution means.` In the "preferredembodiment shown in the drawing, a trough l19 is provided completelyencircling the inner wall of the reactor and provision is `made tomaintain this trough fullof liquid propylene and overflowing so that acontinuous film of liquid propylene is maintained on the inner wall ofseparation section 11. The rising vapors passing upwardly through the"spray, of liquid propylene are are further-contacted withliquidpropylene.;*Liquid'propylenef-allringfrom! reliure-'sectionv 12 isdirected by the outer slopeJ of'bale l20irito trough 1,9 sotha't thetrough is always maintained'veriiowing." Batlle 20 is supported withinthe vapor space of the reactor immediately below the reiiux section andabove spray 18 by support members 21. K r

In an alternative embodiment, reflux section' V12 contains in place'ofthe packing material a partial condenser throughwhich a coolingmedium iscirculated in order to condense a'portion of the rising'vapors byindirect heat exchange. vTherising vapors are brought in contact withthe condensed liquid in countercurrentflow as the vapors l'ow throughthe partial condenser. The contact between the liquid propylene and thevapors serves to remove any polymer which has escapedseparation fromtherising vapors in the-separationsection.

-'Propylene vaporis removed overhead from the top `of refluxsection 12Vthrough conduit -22 and is passed Y throughrconduit 23, blower 24an'dthenl through'conduit v2( to the bottom of reactionfsectionblo.Makeuphydrogen which is addedas required can Lbe introducedv to conduit26 with the recycle propylenevapor through conduit 27. Additional freshpropylene can also be added in the form of vapor to provide the'desired.- agitation in the body of liquidY propylene in reaction section10. Dispersion plate l28 is disposed ltransversely inthe bottom ofreaction section 10 abovethe'inlet of the propylene vapor entering byway of conduit 26. kThis dispersion plate diffuses the incomingpropylene Vvapor anddistributes it'throughout `the cross section'of theAreactor'so that full agitation in all-parts of the vessel is obtained.AThe amount'of' vapor circulated-in` this manner depends upon-the:numberof factors, such as the desired'agitation within the 'reactionsection, the amount of vapor which is removed from the reilux`v section*which lin f turn 'depends "upon 'the amount of vaporization required iinboilingv the liquid propylene j to obtain 'the desired reactiontemperature,` and the a'rn'ountfof reflux condensate required to coolthe reaction mixture.

As shown in -the drawing, the vapor in conduit 22 which `is notrecirculated to the bottom of the reactor is passed by way-of conduit 29to partial condenser 30. Since hydrogen is present in the vapors,it'cannot be expected `thatallrof the vapor introduced to condenser 30is condensed so that provision isimade-forventing'the condenser by wayof conduit 31, andiblower 32 returns thevented *gases by-'way ofconduitSS-to conduit 23 which feeds vinto blower 24 and recirculatingconduit 26. Condensate 'from'l condenser'passes by way ofco'nduit 3'4 toreceiver 3,6 `and then through conduit 37,' pump 38 and conduit '39 `todistributor ring '40 disposed in the top of reflux section 12'abovethe'packingrnaterial. Depending upon the temperature at which thereactor is operated, a

" refrigerant may' have to be us'ed as the cooling media in heatexchanger 30. Ordinarily it is desirable to keep the temperature'of thereflux propylene about 10 to'30 cooler than the desired ytempted-alturein the reactor. y

As the polymerization proceeds,` the solid polymerv formed tends -tosettle into settling leg 41 in which is maintained a relativelyquiescent zone to'v encourage polymer settling'at a'rate of aboutU 0.1to 3 feet'per minute, and an efuent containing a major amount of polymersolids is withdrawn from the bottom of settling leg 41 and passed intothe inlet of compression auger 42. vCompression auger 42 is constructedso as to provide la restriction to the llow ofV polymer at-its dischargeend thereby building up a compacted mass of polymer. i Liquid propyleneis expressed from the mass and forced back through the polylmer and intosettling leg 41. Eiuent can thus be removed from the discharge outlet 43of compression auger 42 containing only about percent liquid. Freshpropylcne can be introduced into auger 42 at an intermediate pointtherewashed with isopropyl alcohol for removal ot catalyst and thendried by Contact with an inert gas. The flow of materials is shown inthe material balance in the following table with reference to the streamflows as indicated in the accompanying drawing.

Material balance (lbs. per hour) Propyl- Fresh Hydro- Over- Recircu-Vent Reactor Reactor ene Feed Catalyst gen head lated: Gas ReuxEffluent, (1G) (17) Makeup Vapor Vapor (31) (37) (43) Propylene 4, 3009S, U76 62, 618 60S 35, 458 390 Propane 43 10, 898 6, 958 68 3, 943 43Diethylaluminum Chloride 1.3 1.3 Titanium Trichloride 5. 5. 6 Hydrogen-0. 05 58 48 10 0. O5 N-Decane 2 2 Polypropylene 3, 714 Soluble Polymer196 of and/or at a lower point of settling leg 41 to passcountercurrently to the polymer in the settling leg and in the auger,thereby washing catalyst back into the reactor. The screw of compressionauger 42 is powered by motor 44. Settling leg 4i should be disposedtoward one side of the reactor and preferably is adjacent the shell ofreactor section 10. The length of the settling leg should be su'lcientto provide a quiescent zone which is not affected substantially by theturbulence within the reactor. Generally, a settling leg having a lengthto diameter ratio in the range of about 3:1 to 10:1 and preferably about5:1 to 8:1 provides the required settling rate. The settling leg shouldbe cooled by circulating a coolant through jacket 46 in order to preventboiling oi the propylene in the settling leg.

In order to illustrate further the method of my invention, the followingexample is presented. The conditions and proportions presented in theexample are meant to be typical only and should not be construed tolimit my invention unduly. Liquid propylene is contacted with a catalystof diethylaluminum chloride and titanium trichloride in a verticallyelongated reaction Zone 8 feet in diameter and 40 feet in length at atemperature or" 100 F. and a pressure of 250 p.s.i.a. Fresh propylene isintroduced as aspray in the vapor `space above the boiling liquidpropylene and a continuous film of liquid propylene is maintainedflowing downwardly over the inner walls of the reaction column in thisvapor space. Vapor rising from the boiling liquid propylene is passed incontact with the spray of incoming liquid propylene and then upwardlythrough a 10 foot section of the reaction tower containing 1%. inch Berlsaddles. Propylene vapors are withdrawn overhead and a portion isrecirculated to the bottom of the reaction zone and the remainder ispassed through a condenser wherein the propylene is condensed and thecondensate returned to the reiiux section ofthe reactor and distributedover the top of the packing. The polymer solids are withdrawncontinuously from the bottom of the reactor through the settling leg andcompression auger. The temperature of the propylene condensate inreceiving vessel 36 is 80 F. and the pressure in said vessel is 235p.s.i.a. Cooling water at 60 F. is circulated through a jacketsurrounding the settling leg so that the temperature therein ismaintained at 80 F., thereby eliminating any vaporization of propylenein the settling leg and maintaining the lower portion thereof in aquiescent state. The polymer solids withdrawn from the compression augerare As will be apparent to those skilled in the art, variousmodifications can be made in my invention without departing from thespirit or scope thereof.

I claim:

A reactor suitable for propylene polymerization comprising, incombination, an upright cylindrical shell having a lower reactionsection with a length to diameter ratio in the range or about 3:1 to10:1, an intermediate separation section with a length to diameter ratioin the range of about 1:1 to 5:1, and an upper relluX section, top andbottom closure members coniining the volume within said shell, acircular trough disposed in said separation section adjacent said shellso that liquid overflowing from said trough is distributed against theinner wall of said shell in said separation section, vapor-liquidcontact packing material positioned in said reilux section, means forcirculating vapor from the top of said rellux section to an inlet in thebottom ot said reaction section, a dispersion plate positionedtransversely in the bottom -of said reaction section above the vaporinlet, means for condensing vapor withdrawn from the top of said refluxsection and distributing the resulting condensate over said packing,batl'le means positioned below said packing and above said trough todirect a portion of liquid owing from said packing into said trough, aspray for liquid feed disposed in said separation section, a catalystsettling leg vertically disposed adjacent said shell and at the bottomof said reaction section, said settling leg having a length to diameterratio in the range of about 3:1 to 10:1, and a compression augerconnected at its inlet end to the lower end of said settling leg.

References Cited by the Examiner UNITED STATES PATENTS 2,085,524 6/37Simo 260-949 2,484,384 10/49 Levin et al. 260-683.15 2,755,324 7/56Mueller 260-683.l5 2,885,389 5/59 Schappert 260-94.9 2,904,409 9/59Bolstod 23-285 3,002,961 10/61 Kirschner 26093.7 3,023,203 2/62 Dye260-94-.94 3,126,365 3/64 Hooker 260-911-.92

IOSEPH L. SCHOFER, Primary Examiner.

MILTON D. LIEBERMAN, WILLIAM H. SHORT,

Examiners.

